Hi, I'm Junya, engineer of Hatena.
I was very grad to read your detailed report.
We don't use Catalyst, but we use our MVC framework called "Hatena Framework" which we made by ourselves.
Naoya made a presentation about our backend system on YAPC.
http://d.hatena.ne.jp/naoya/20060404/1144121846
These slides don't include much about the framework, but you can see more about our systems.
Thank you.